This invention relates to fuel injection nozzles for supplying fuel to compression ignition engines and of the kind comprising a fuel pressure actuated valve member which is engageable with a seating to prevent flow of fuel through an outlet orifice located downstream of the seating from a fuel inlet, a first coiled compression spring acting on the valve member to bias the valve member into engagement with the seating, a pre lift stop engageable by a surface moveable with the valve member after the valve member has moved to a predetermined position away from the seating, and a second coiled compression spring acting on the pre lift stop whereby continued movement of the valve member away from the seating beyond said predetermined position takes place against the action of both springs.
Such nozzles are well known in the art and may be of the sac type or pintle type. The initial movement of the valve member to the predetermined position allows for a restricted flow of fuel through the outlet to the associated engine, the rate of flow increasing as the valve member is moved beyond the predetermined position by an increase in the pressure of fuel at the inlet.
When the fuel pressure at the inlet falls the valve member moves to the closed position initially under the action of both springs but finally under the action of the first spring only and it is found that the valve member can "hang" at the position where the second spring becomes ineffective. This is undesirable because rapid closure of the valve member is required to prevent fuel dribble which might result in increased exhaust emissions.